This invention relates to an electrostatic copier which automatically feeds and delivers documents to be copied.
In order to copy a plurality of documents with a conventional copier, each document should be manually set on a platen glass located in the upper portion of the apparatus, and also removed from the platen glass to be replaced by the next document. However, this exchange of the documents is a very troublesome job when copying many documents.
Recently a new apparatus, which is called an automatic document feeder, has been developed. The procedure of feeding documents by the automatic document feeder will be described as follows. After a plurality of documents to be copied are set at a prescribed position on the automatic document feeder, the documents are automatically conveyed sheet by sheet onto the prescribed position on the platen glass. The document is exposed on the platen glass. After exposure, the document is automatically delivered. The automatic document feeder is used either as a built-in device of the copier or as an optional accessory to the conventional copier as occasion demands.
The procedure of copying a plurality of documents by an electrostatic copier equipped with this kind of automatic document feeder is as follows. A plurality of documents to be copied are initially stacked at the prescribed position on the automatic document feeder and the copy button, which is mounted on the operation panel of the copier, is pressed. Then, the document feeding mechanism of the automatic document feeder is activated and a sheet of document, the uppermost or the lowermost of a pile of documents on the document feeder, is conveyed onto the platen glass. The conveyed document is stopped at the prescribed position on the platen glass by the stopping device which protrudes a little from the platen glass surface. After the document is thus aligned at the prescribed position on the platen glass, the optical scanning unit installed just below the platen glass moves and exposes the document from the underside to the light of a lamp. The reflected light from the document is projected on the surface of the photoreceptor. Then, a document image is formed by a series of electrophotographic processes. Likewise afterward, each of the documents are automatically conveyed and processed as described above.
This type of copier is usually designed to copy those documents belonging to a predetermined size group, as an example B5 and A4, the upper size limitation of this size group being A4 here.
And problems are caused by a careless setting of a document which is longer than the upper size limitation, which we call long document hereafter in the specification, to the document feeder. In this case, when the copying operation starts, the long document is conveyed onto the platen glass, and after the leading edge of the document is halted by the stopping device, the trailing portion of the document is still conveyed by the feed roller. As a result, the leading edge of the document is damaged or the trailing portion of the document is bent and wound around the feed roller, which may cause jamming of the apparatus in addition to damage of the document.